[8.06] Confusion limits on Spectra taken with the Next generation Space Telescope Near-Infrared Multi-Object Spectrograph

The Ad hoc Science Working Group has recommended
(US-manufactured) micro-electronic mirrors or shutters
(MEMS) as the preferred slit-generating system for the Next
generation Space Telescope near-infrared multi-object
spectrograph that will be supplied by the European Space
Agency. Such MEMS devices will not be perfectly `binary' in
the sense that elements which are in the `off' position will
still deliver some light to the spectrograph from bright
objects in the FoV via diffraction and scattering processes.
These `spoilers' will appear as attenuated spectra on the
detector and some of them will overlap the spectra of the
faint target sources. We have used source counts, size and
magnitude distributions derived from the deepest NICMOS
observations of the Hubble Deep Fields to estimate the
expected frequency and degree of such overlaps. We also
simulated a deep exposure with a MEMs based spectrograph
using SLIM - a multi-object spectroscopy simulator
originally developed for the slitless spectroscopy modes of
the HST Advanced Camera for Surveys - adapted to handle a
mixture of targets and attenuated spoilers. The results are
compared with estimates of this confusion problem discussed
by several groups during the NGST spectrograph studies.

The author(s) of this abstract have provided an email address
for comments about the abstract:
wfreudli@eso.org